Reticles, wafers, and other semiconductor substrates and the like have very high cost. Exposure to air brings with it the risk of contamination and damage to the substrate, so vacuum environments are commonly used in processing, handling, and using these substrates. While it is possible to store substrates within a vacuum processing environment for short durations, this consumes valuable in-vacuum space and is not generally suitable for longer term storage, particularly where numerous substrates (e.g., the hundreds of reticles that might be needed in a wafer stepper). This approach is also unsuitable where transfer is required between separate vacuum processing environments.
Batch transfer techniques such as multi-wafer carriers have long been employed to transfer wafers among processing systems. In addition, the storage of individual substrates in tightly sealed boxes either under atmospheric or vacuum pressure conditions or under inert environments such as Nitrogen or Argon has been used in the past. However to the present day, these storage boxes require the box to be opened and the substrate to be exposed to a regular air environment, while the substrate is being transferred from the box to a working environment.
There remains a need for single-wafer storage and transportation alternatives that permit transfer of substrates while reducing exposure to the harmful effects of contamination from airborne particles and particles that might be disturbed during pumping and venting cycles.